Kumi

Try the interactive demo →

Kumi is a declarative DSL for building calculation systems.

Schemas define:

• Input shape (scalars, arrays, nested structures)
• Declarations (computed values and boolean conditions)
• Dependencies between declarations

The compiler:

• Performs type checking
• Detects unsatisfiable constraints
• Determines evaluation order
• Generates code for Ruby or JavaScript

Calculation systems appear in: tax engines, pricing models, financial projections, compliance systems, insurance underwriting, shipping rate calculators.

Status: experimental. Public API may change. Typing and some static checks are still evolving.

Feedback: have a use case or hit a rough edge? Open an issue or reach out (andremuta+kumi@gmail.com).

• US Tax Calculator (2024) — a single schema computes federal, state, and FICA taxes across multiple filing statuses. Open in the demo.
• Monte Carlo Portfolio — demonstrates probabilistic simulations and table visualizations. Open in the demo.
• Conway's Game of Life — showcases array operations powering a grid-based simulation. Open in the demo.

gem install kumi

Requires Ruby 3.1+. Runtime dependencies: mutex_m and zeitwerk (bundled via Rubygems).

require 'kumi'

module Double
  extend Kumi::Schema

  schema do
    input { integer :x }
    value :doubled, input.x * 2
  end
end

# Execute in Ruby
result = Double.from(x: 5)
result[:doubled]  # => 10

# or just call the method directly
Double._doubled(x: 5) # => 10

# Export to JavaScript (same logic)
Double.write_source("output.mjs", platform: :javascript)
# ./output.mjs
# export function _doubled(input) {
#   let t1 = input["x"];
#   let t3 = t1 * 2;
#   return t3;
# }

You can also override the compilation strategy without touching code by setting KUMI_COMPILATION_MODE to jit or aot (e.g. export KUMI_COMPILATION_MODE=aot).

Try the interactive demo (no setup required).

• Syntax Reference - DSL syntax, types, operators, functions, and schema imports
• Functions Reference - Auto-generated docs for all functions and kernels
• functions-reference.json - Machine-readable format for IDEs (VSCode, Monaco, etc.)
• Development Guide - Testing, debugging, and contributing

To regenerate function docs: bin/kumi-doc-gen

MIT License. See LICENSE.